The Shia, it said, were poised to spread "their insidious beliefs" to Baghdad and Sunni-dominated areas of Iraq.

Zarqawi claims to have masterminded several attacks on Shia targets, including a car-bombing in 2003 that killed Ayatollah Muhammad Baqr al-Hakim, former leader of one of Iraq's two main Shia parties.

A message attributed to Zarqawi earlier this week accused the Shia of taking part in the US assault on the Sunni Muslim city of Falluja and described their spiritual leader, Ayatollah Ali Sistani, as "Satan".

Iraqi interim Prime Minister Iyad Allawi has meanwhile told the BBC's Breakfast with Frost programme he believes the polls will eventually spell the end of violence in Iraq.

But, he said, this will not happen immediately and insurgent attacks are likely to continue in the short term.

The interim government has announced sweeping security measures to protect voters in the 30 January election.

Curfews will be extended

In many areas, election staff intend to keep the location of polling stations secret until the last minute

Iraq's borders will be closed for three days around the election

Baghdad's airport is to be closed for two days

The movement of pedestrians and cars close to polling stations will also be restricted, and non-official cars will be prevented from travelling between Iraq's 18 provinces